Rear Pre-Safe (R), Function - GF30.30-P-0015FH
Model 238
Up To Model Year 2021
With Code 23P (Drive package)
Show on model 238
Function requirements, general
- No undervoltage or overvoltage
- Engine running or drivetrain operational:
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" or "Drivetrain operational" signal to the Intelligent Drive control unit via drive train CAN, powertrain control unit and chassis FlexRay.
- No trailer recognized (with CODE 550 (Trailer hitch))
The trailer recognition control unit (with code 550 (Trailer hitch)) sends the "Trailer recognized" status via the interior CAN, electronic ignition lock control unit and chassis FlexRay to the Intelligent Drive control unit.
Rear end PRE-SAFE®, general
The rear end PRE-SAFE® function extends the preventative occupant protection system in dangerous situations associated with following traffic. The rear bumper radar sensor on the outer right and left detect the traffic behind one's own vehicle. The Intelligent Drive control unit analyzes the information provided by the rear bumper radar sensors on the outer right and left to determine the closing speed of and distance to following traffic. Various measures are introduced on this basis that may be able to reduce the consequences of an accident for the vehicle occupants.
The possible measures are shown in chronological order in the following graphic:
Shown on model 238.3
The rear end PRE-SAFE® function consists of the following subfunctions:
- Function sequence for vehicle detection and warning about the traffic to the rear (Escalation level t 1 )
- Function sequence for preparing the stationary vehicle for a collision (escalation level t 2 )
- Function sequence for activating the occupant protection measures (escalation level t 3 )
- Function sequence for securing the vehicle after the collision (escalation level t 4 )
Function sequence for vehicle detection and warning about the traffic to the rear (Escalation level t 1 )
Impact in approx. t = 1, 4 s:
If an approaching vehicle is detected by the right and left rear outer bumper radar sensor and is deemed accident-critical by the Intelligent Drive control unit, the driver of this following vehicle is warned by activating the rear hazard warning flasher function (except CODE 494 (USA version) and except CODE 460 (Canada version)).
The flashing frequency of the rear turn signal indicator is f = 5 Hz.
Technical implementation
The Intelligent Drive control unit reads in the signals from the rear bumper radar sensors on the outer right and left via the radar CAN 2, evaluates them and sends the request for outputting a warning via chassis FlexRay, electronic ignition lock control unit and interior CAN to the front SAM control unit (except CODE 494 (USA version) and except CODE 460 (Canada version)). This evaluates the incoming request and activates the function rear end hazard warning flasher.
Additional function requirements for preparing the standing vehicle for a collision (escalation level t 2 )
- Vehicle at rest
- Brake request detected by actuating the brake pedal or actuating the parking brake or by engaging gear range "P" The Electronic Stability Program control unit sends the status of the braking system via the chassis FlexRay to the Intelligent Drive control unit.
The Electronic Stability Program control unit activates the parking brake and sends the status of the electric parking brake switch via chassis FlexRay to the Intelligent Drive control unit.
The fully integrated transmission control unit sends information about the selected gear range via drive train CAN, powertrain control unit and chassis FlexRay to the Intelligent Drive control unit.
- The brake request is transmitted from the hold function or the DISTRONIC interval pilot (with code 23P (Driver Assist Package Plus))
- Brake request detected by actuating the brake pedal or actuating the parking brake or by engaging gear range "P" The Electronic Stability Program control unit sends the status of the braking system via the chassis FlexRay to the Intelligent Drive control unit.
- The vehicle is braked to a standstill by the DISTRONIC interval pilot (with code 23P (Driver Assist Package Plus))
The Electronic Stability Program control unit calculates the vehicle speed from the wheel speed signals and sends this via the chassis FlexRay to the Intelligent Drive control unit.
Function sequence for preparing the stationary vehicle for a collision (escalation level t 2 )
Impact in approx. t = 300 s:
If the Intelligent Drive control unit registers no or only inadequate deceleration of the approaching vehicle over the closing speed, the vehicle is "firmly braked" by increasing the brake pressure as a preventive measure. The hard braking on the one hand significantly reduces the occupant load (whiplash), while on the other hand serves the protection of other road users. Uncontrolled movements of the vehicle after a rear end collision, which can lead to subsequent collisions, are reduced (collision with a vehicle directly ahead, collisions with pedestrians or another road user in crossing situations).
Technical implementation
The Intelligent Drive control unit sends the brake request via chassis FlexRay to the Electronic Stability Program control unit, which then actuates the traction system hydraulic unit accordingly.
Function sequence for activating the occupant protection measures (escalation level t 3 )
Impact in about t = 100 to 50 ms:
If the Intelligent Drive control unit calculates that a rear-end collision is probable using the closing speed of the approaching vehicle, preventive measures designed to provide protection to occupants are initiated. The driver and the front passenger are held in position in their seat in order to optimize the protective effect of the conventional restraint equipment.
Technical implementation
The Intelligent Drive control unit transmits the following information via the chassis FlexRay to the Electronic Stability Program control unit:
- Closing speed of the vehicle to the rear
- Time until the possible impact of the vehicle to the rear
- Deployment recommendation for the front reversible emergency tensioning retractors
The Electronic Stability Program control unit initiates PRE-SAFE® measures to provide protection to occupants.
Function sequence for securing the vehicle after the collision (escalation level t 4 )
About t = 2 s after an impact:
Brake pressure continues to be applied for approx. t = 2 s after a rear-end collision.
Technical implementation
The technical implementation of "Maintain brake pressure" corresponds to the technical implementation of the escalation level t2 .
After a rear-end collision, the rear end PRE-SAFE® function is no longer available until it is activated using a diagnostic tester.
| Electrical function schematic for PRE-SAFE® rear end | PE30.30-P-2061-97DCA | ||
| Overview of system components for driver assistance systems | GF54.00-P-9998FH |